Purpose The purpose of this study was to determine changes in muscle tone, respiratory function, and blood pressure depending on posture when using a smartphone. Methods 51 female college students in their 20‘s who voluntarily agreed to participate in this study were selected as subjects. The subjects used their smartphones for 15 minutes each in three postures: sitting with crossed one’s legs, stooped posture, and elbow support posture. For quantitative analysis, muscle tone(upper trapezius muscle, erector spinae muscle), respiratory function(inspiratory competence, inspiratory flow velocity, inspiratory flow volume), and blood pressure(systolic, diastolic) were measured a total of 4 times before and after using the smartphone in 3 postures. Results In the changes of muscle tone, there was a statistically significant difference in the upper trapezius muscle in the three postures compared to pre-test. There was a statistically significant difference in the muscle tone of the erector spinae muscles in the stooped posture and the elbow support posture compared to pre-test. In changes of respiratory function, there was a statistically significant difference in inspiratory competence and inspiratory flow volume in the elbow support posture compared to pre-test. Conclusion According to the results of the study, it was found that using a smartphone in a poor position for more than 15 minutes had an adverse effect on muscle tension and respiratory function. Therefore, future studies are expected to require studies that consider various sociodemographic characteristics and conduct physiological and pathological analyses of using smartphone.